Cryptography

Overview A digital signature is a cryptographic value that proves a specific piece of data is authentic and unaltered, generated by encrypting a hash with a private key. A digital certificate is a CA-issued document that binds a public key to an identity, giving others a trusted way to know whose key they’re using. Confusing the two leads to designs that either can’t verify who signed something or can’t verify what was actually signed. ...

Overview Hashing and encryption both scramble data into something unreadable, but they solve different problems: hashing is a one-way function used to verify that data hasn’t changed, while encryption is a reversible process used to keep data secret from unauthorized parties. Mixing them up — like encrypting passwords instead of hashing them — is a common and dangerous mistake. Comparison Diagram HashingEncryptionInput (any length)Hash FunctionDigest (fixed length)irreversible, no keyPurpose: integrity & verificationPlaintextEncrypt (+ key)CiphertextDecrypt (+ key)Plaintext (recovered)Purpose: confidentiality Comparison Table Aspect Hashing Encryption Core operation Transforms input into a fixed-length digest Transforms plaintext into ciphertext Reversibility One-way; original input cannot be recovered Two-way; ciphertext decrypts back to plaintext Key requirement No key needed for a standard hash function Requires a secret key (or key pair) Output size Fixed-length digest regardless of input size Ciphertext length scales with plaintext size Determinism Same input always produces the same digest Same plaintext yields different ciphertext each run via IV/nonce Primary goal Integrity verification and data identification Confidentiality of data Main failure mode Collision: two inputs producing the same digest Key compromise, exposing all encrypted data Typical use cases Password storage, checksums, digital signatures Securing data at rest and in transit Key Differences Hashing is one-way; encryption is designed to be reversible with the correct key. Encryption always requires a secret key; standard hashing needs none. A hash always produces a fixed-length digest, no matter how large the input is. Hashing protects integrity; encryption protects confidentiality. A hash function must resist collisions; a cipher must resist key or plaintext recovery. When to Use Each Hashing ...

Overview Symmetric encryption uses a single shared secret key for both locking and unlocking data, making it fast but dependent on securely distributing that key beforehand. Asymmetric encryption uses a mathematically linked key pair — public and private — solving the distribution problem at the cost of heavier computation. Comparison Diagram SymmetricAsymmetricAliceBobsame keyshared secretlySenderReceiverpublic key(shared openly)private key(kept secret)encrypted withpublic key1 key, both directions2 keys, one direction each Comparison Table Aspect Symmetric Encryption Asymmetric Encryption Key setup One shared secret key generated for both parties Mathematically linked key pair: public key and private key Key distribution Requires a secure channel to exchange the key beforehand Public key can be freely published; private key never leaves its owner Encryption operation Same key encrypts the plaintext Sender encrypts using the recipient’s public key Decryption operation Same key decrypts the ciphertext Recipient decrypts using their own private key Performance Fast, low CPU overhead, suited to large volumes of data Computationally expensive, orders of magnitude slower Key scalability Number of keys needed grows quadratically with participants Each participant needs only one key pair regardless of participant count Common algorithms AES, ChaCha20, 3DES RSA, ECC, Diffie-Hellman Typical use case Bulk data encryption: disks, files, VPN tunnels Key exchange, digital signatures, certificate/identity verification Key Differences Symmetric uses a single shared key; asymmetric uses a key pair of public and private keys Symmetric is far faster, making it practical for encrypting large payloads Asymmetric eliminates the key distribution problem since the public key can be shared openly Real-world protocols like TLS use a hybrid approach, using asymmetric encryption to exchange a symmetric session key Only asymmetric keys support digital signatures for authenticity and non-repudiation When to Use Each Symmetric Encryption ...